Erin Fox, associate chief pharmacy officer of University of Utah Health, told CBS MoneyWatch, that most of the drugs in short supply are generic, older products, and around half are injectable drugs that require more stringent manufacturing processes.

There are myriad reasons for the hundreds of drug shortages now facing doctors and patients, many of which remain unclear. But, as Ars has reported before, the root cause of shortages of low-cost, off-patent generic drugs is well established. These drugs have razor-thin to non-existent profit margins, driven by middle managers who have, in recent years, pushed down wholesale prices to rock-bottom levels. In some cases, generic manufacturers lose money on the drugs, disincentivizing other players in the pharmaceutical industry from stepping in to bolster fragile supply chains. Several generic manufacturers have filed for bankruptcy recently.